I a currently building a fender 5e3 guitar amp. The schematic has the heater circuit completed with one loop of the circuits (for all but the rectifier tubes) via ground. In other words, one wire coming out of the transformer is grounded, with the other wire looping across the heater elements with the other pin of the heater grounded ,thus completing the circuit.

In my audio amps, I have always run two heater wires to each tube and twisted them tightly and I was planning to do this for this amp. Then I began to wonder why the fender people did it as described above. Was it simply a money saving exercise and how did they get away with it without hum? Indeed, should I twist or should I stick to the original design?

Input appreciated.

Cheers,

Rob

PS, I have attached a picture of a slightly different model showing the layout just to demonstrate what I am talking about

I probably was not clear enough. Of course, if I were to run separate wires I would twist as per usual, my question should have read - do I have to run separate wires at all - does it make a difference to this amp?

My initial thoughts were that Fender designed it the way they did to cut costs and labor. My thoughts were to run separate twisted wires to reduce hum, but not being a guitar amp person (I am making it for my son), It then occurred to me that there might be (although I can't think what) some functional reason to use the chassis as one path of the heater current?

DON'T run heater current through the chassis... I doubt Fender did - a lazy draftsman probably just used the ground symbol instead of showing the actual connections. If heater circuit is connected to chassis, it should only be in ONE place. If there's one rule for making a quiet amplifier, it's to provide a return circuit for every current - don't allow high currents to share a path with signals.

Thanks Zigzagflux, that's what I will do. Do you think that I should ground my virtual center tap through a capacitor or just directly?

Hi Tom, this is what I initially thought but everything that I can see suggests otherwise. If you look at that particular drawing which is supposed to be an accurate layout wiring layout, they have grounded one heater wire (green) with the B+ center tap. Perhaps these guitar amp people don't worry so much about hum! I agree with you though, I am not going to do it this way.